I have a MBP A1278 Mid-2010 that a friend has asked me to try to repair. At first it sounded like a simple battery/SMC reset sort of fault but I'm having trouble working out exactly what's wrong with it now.

So, the MBP was not used for around 6 months and in that time the battery swelled. The swelling damaged the trackpad but otherwise doesn't appear to have caused further cosmetic damage. I am not sure if this could have caused any damage to the logic board, DC-in board or any components but a new battery was purchased and the Mac worked fine for 4 weeks.

I am unsure if any OS update took place in that time but suddenly the Mac stopped booting up properly.

I initially tried to power cycle the device by disconnecting the power adapter and battery and holding the power button but nothing improved.

Powering the laptop with the battery connected causes the white power light to come on but then it will cycle reboot every 20 seconds until the power button is held or Shift-Ctrl-Opt power is pressed. Just white power light, then click and reboot. No chime, no beep.

Powering the laptop with the battery and the magsafe adapter connected (which displays a solid green light) causes the white power light to come on, the battery status indicator works (displays full battery), the fans spin up to what seems like 100% battery, but nothing else happens, no chime, screen stays black, nothing happens.

A Shift-Ctrl-Opt Power with the adapter connected causes the laptop to power up, reboot once then continue to stay powered and spin fans as above.

I removed the RAM (2x2GB), the Mac rebooted itself every 20 seconds once powered on, but did not beep to indicate an error. I returned the RAM, no improvement.

I've checked HDD and optic drive connectors are seated correctly.

One thing that is confusing me is related to the battery status/charger status, currently while the macbook is on, when the test button is pressed, the battery status light shows 8 solid green lights, connect the adapter and that also displays a solid green light. Power off the mac and the battery status test shows 7 solid lights and 1 blinking light, and the adapter light turns orange, so charging. It stays orange but the battery status also always shows full battery. Does the charging state normally depend upon whether the laptop is powered on and would it normally charge while showing "full power"?

Any further advice regards working out the problem with the device or which component could be at fault? What could have been damaged by the swollen battery?

Update (01/26/2018)

To update this, I have confirmed the magsafe charger is working.

I have replaced the DC-In board and the charger and laptop are now behaving as expected. The magsafe adapter lit up immediately, went orange, charged the battery to full then went green.

The MB still emits the same behaviour as before though, albeit more consistently;

If you press the power button, it turns on showing little sign of life. After 20 seconds it makes a loud click and turns off. After ~5 second delay it powers back on and stays on, the fans spin up to full speed but there is no further activity, no chime, no beeps, no screen activity. I have left it like this for 20 minutes and nothing changed. The power button must be held to turn it off.

It is seeming more and more as though this will need a replacement logic board.

Sorry, perhaps I worded that poorly. The battery status lights do not stay on, I meant that was the status shown when the test button is pressed.

Regardless, I have detached the magsafe adapter and battery, disconnected the battery test ribbon and reconnected the battery and adapter. The adapter is still a solid orange while the macbook is powered down, turns green while on, and back to orange when off, yet I don't believe the battery requires further charging.

To be clear if you press the battery checker you either see all of the LED's lit or a group of them and the last one is blinking. Then after you release your finger the LED go out. This is normal operation for the tester and it's telling us the Battery is either charged or slightly discharged. Plugging in or disconnecting a powered MagSafe adapter will also enable the battery tester. A single blinking LED at the end of a group of LED's is a battery which is charging. We can think if the MagSafe as being the last LED in the tester Amber when any of the 7 LEDs of the 8 is lit and Green when the 8th LED is lit.

I've now left the battery to drain overnight. The battery test indicates a single blinking light, and now the macbook doesnt boot up and the magsafe charging indicator doesn't come on either. I tried an SMC reset (removed battery and magsafe, held power for 10s, reconnected both) but nothing still.

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